It has long been desired to interchangeably use methane, hydrogen or mixtures of methane and hydrogen as cryogenic liquids or compressed gases in place of gasoline in spark-ignited engines. But this goal has not been satisfactorily achieved, and as a result, the vast majority of motor vehicles remain dedicated to petrol even though the costs of methane and many forms of renewable hydrogen are far less than gasoline. Similarly it has long been a goal to interchangeably use methane, hydrogen or mixtures of methane and hydrogen as cryogenic liquids and/or compressed gases in place of diesel fuel in compression-ignited engines but this goal has proven even more elusive, and most diesel engines remain dedicated to pollutive and more expensive diesel fuel.
Conventional spark ignition systems include a high voltage but low energy ionization of a mixture of air and fuel. Conventional spark energy magnitudes of about 0.05 to 0.15 joule are typical for normally aspirated engines equipped with spark plugs that operate with compression ratios of 12:1 or less. Adequate voltage to produce such ionization must be increased with higher ambient pressure in the spark gap. Factors requiring higher voltage include leaner air-fuel ratios and a wider spark gap as may be necessary for ignition, increases in the effective compression ratio, supercharging, and reduction of the amount of impedance to air entry into a combustion chamber. Conventional spark ignition systems fail to provide adequate voltage generation to dependably provide spark ignition in engines such as diesel engines with compression ratios of 16:1 to 22:1 and often fail to provide adequate voltage for unthrottled engines that are supercharged for purposes of increased power production and improved fuel economy. These issues also plague alternative or mixed fuel engines.
Failure to provide adequate voltage at the spark gap is most often due to inadequate dielectric strength of ignition system components such as the spark plug porcelain and spark plug cables. High voltage applied to a conventional spark plug, which essentially is at the wall of the combustion chamber, causes heat loss of combusting homogeneous air-fuel mixtures that are at and near all surfaces of the combustion chamber including the piston, cylinder wall, cylinder head, and valves. Such heat loss reduces the efficiency of the engine and may degrade the combustion chamber components that are susceptible to oxidation, corrosion, thermal fatigue, increased friction due to thermal expansion, distortion, warpage, and wear due to loss of viability of overheated or oxidized lubricating films.
In addition, modern engines lack electrical insulation components having sufficient dielectric strength and durability for protecting components that must withstand cyclic applications of high voltage, corona discharges, and superimposed degradation due to shock, vibration, and rapid thermal cycling to high and low temperatures. Similarly, the combustion chamber of a modern diesel engine is designed with very small diameter ports for a “pencil” type direct fuel injector that must fit within the complex and tightly crowded inlet and exhaust valve operating mechanisms of a typical overhead valve engine head. A typical diesel fuel injector's port diameter for entry into the combustion chamber is limited to about 8.4 mm (0.331″). In addition to such severe space limitations, the hot lubricating oil is constantly splashed in the engine head environment within the valve cover to heat the fuel injector assembly to more than 115° C. (240° F.) for most of the million-mile life requirement, which prohibits application of conventional air-cooled solenoid valve designs.
It is highly desirable to overcome requirements that limit diesel engine operation to compression ignition and the use of diesel fuel of a narrow cetane rating and viscosity along with strict requirements for elimination of particles and water. The potential exists for more plentiful fuel selections with far less replacement cost wherein the fuels have a wide variation in cetane and/or octane ratings along with impurities such as water, nitrogen, carbon dioxide, carbon monoxide, and various particulates.
In order to provide smooth transition from economic dependence upon fossil fuels is highly desirable to enable interchangeable utilization of conventional diesel fuel or gasoline along with renewable fuels such as hydrogen, methane, or fuel alcohols. Improved insulators are required in instances that diesel fuel is to be utilized by application of sufficient plasma energy to the diesel fuel as it enters the combustion chamber to cause very rapid evaporation and cracking or subdivision of diesel fuel molecules, and production of ignition ions to thus overcome the formidable problems and limitations of compression ignition.
Accordingly, there is a need in the art for improved insulators and materials and method of manufacture and use, for example, materials with improved durability and dielectric strength for use in ignition system components for multifuel engines.